function loader(source) {
  //调用async方法,可以把loader执行从同步改成异步
  //改成异步之后,当前的loader执行结束后并不会立刻向下执行下一个loader
  //需要你手工的在代码调用callback方法
  let callback = this.async();
  console.log(new Date());
  setTimeout(() => {
    callback(null, source + "//async1");
  }, 3000);
  return source;
}
loader.pitch = function(remainingRequest, previousRequest, data) {
  let asyncCallback = this.async();
  //console.log(this);//loaderContext
  console.log("async1-pitch");
  asyncCallback(null);
};

loader.normal = function () {};
module.exports = loader;
